I'm trying to understand this. You want an over all plot which will be consistent, in and of itself, but you want the reader to be allowed to make choices within that plot. Let's ... try an example:
Plot: You are a scientist who has recently discovered and announced that the world is about to end from a giant comet smacking into the earth. You now have 24 hours to live.
Choices: Party with friends until you die ... find love / get laid ... try to get drunk off your ass ... go on a killing spree, exc.
The fact that the comet is hurling towards earth isn't going to change and the amount of time you have isn't going to change, nor is the fact that you are a scientist and that people around you are understandably freaking out. But you get to decide how to spend your time during that period and it will effect your personal ending. Does that sound like what you're trying to do or am I wrong?